Remember when “the dress” broke the Internet in February 2015?  A photo of a nondescript striped dress on Tumblr went viral because it asked a simple question that baffled brains around the world: Is the dress blue and black or white and gold?

The answer to this infamous question was debated over and over again. Why didn’t people agree on the color of the dress? It seems our brains were to blame. This is a great example of an optical illusion where the eyes tricked the brain into seeing something that wasn’t actually there…or was it? Let’s take a closer look.

It all starts in the retina, a thin layer of tissue that lines the back of the eye near the optic nerve.  The optic nerve is made of over one million nerve fibers that are responsible for transmitting images from the retina to the brain. When the eye sees light, it triggers a photochemical reaction in the rods and cones (AKA photoreceptor cells). Rods detect brightness and vision at low light levels, as well as shades of gray. Cones see day vision and the colors red, green and blue.

When someone looks at the photo of the dress, the brain is actually interpreting the background lighting–that bluish tint. If your brain thinks the dress is more illuminated, you see it as blue and black. If your brain thinks it’s more reflective (it’s in shadows), then the dress appears to be gold and white.

It’s not really the dress itself, but the strange lighting that made this an unbelievable optical illusion because the dress seems to be on a perceptual boundary with an almost equal balance of red, green and blue.  In other words, your retinal cones are quite confused!

In person, the dress is actually blue and black, so if you see it as gold and white, it’s because your eyes are subtracting the wrong background colors.

The Cornsweet Illusion, also known as the Craik–O'Brien–Cornsweet Illusion or the Craik–Cornsweet Illusion

If you want to see more examples of how shadows can play tricks on your brain, check out The Cornsweet Illusion, also known as the Craik–O'Brien–Cornsweet illusion and the Craik–Cornsweet illusion pictured above.

In this popular illusion, your brain is confused by the shadowing effect, so it thinks the bottom object is lighter than it is. This phenomenon is called lateral inhibition.

The truth is that the gray squares are the exact same color. Test it out for yourself by placing a finger across the middle to block the part where they meet or look at the picture below.

The Cornsweet Illusion, also known as the Craik–O'Brien–Cornsweet Illusion or the Craik–Cornsweet Illusion

When you saw the dress illusion were you team #TheDressIsWhiteAndGold or #TheDressBlueAndBlack? Let us know in the comments section on the Clear Eyes Facebook page.